JPH02180700A - Dehydration of organic sludge - Google Patents

Abstract

PURPOSE:To enhance the treatment efficiency of sludge by adding an inorg. flocculant to org. sludge and further adding an amphoteric org. polymer flocculant having a specific colloid equivalent value and an anion amount/cation amount ratio thereto before dehydrating said sludge. CONSTITUTION:An inorg. flocculant such as ferric chloride, aluminum sulfate or polyiron sulfate is added to org. sludge to be mixed therewith. Subsequently, an amphoteric org. polymer flocculant having a colloid equivalent value (a-value) of 1.0-3.7meg/g at pH3, a colloid equivalent value (b-value) of -0.35--3.5meg/g at pH7 and a value of an anion amount/cation amount ratio (a-b)a of 1.2-2.0 is added to and mixed with said sludge to perform flocculation. Next, the floc generated by flocculation is supplied to a dehydrator as it is or after separated water is removed to perform dehydration.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for dewatering organic sludge using an inorganic flocculant and an amphoteric organic polymer flocculant.

[Conventional technology]

Conventionally, as a method for dewatering organic sludge generated from the treatment of sewage, human waste, or organic industrial wastewater.

A method of treating sludge by adding an inorganic flocculant and an organic polymer flocculant to sludge has been proposed (Japanese Patent Laid-Open No. 129200/1983).

JP-A-60-129200 discloses a method in which an inorganic flocculant is added, and then an amphoteric polymer flocculant consisting of a composition containing a cationic polymer and an anionic polymer is added for dehydration treatment.

However, since this method sufficiently neutralizes the charge of the sludge, there is a problem in that when the amount of inorganic flocculant is increased, the flocculating property is significantly reduced, making subsequent dewatering treatment impossible.

Furthermore, instead of the above-mentioned cationic polymer and anionic polymer, a method of adding an amphoteric polymer flocculant having a cationic group and an anionic group may also be considered.

In this method, an amphoteric organic polymer flocculant is added to organic sludge whose pH value after addition of the inorganic flocculant is 5 to 8, and then the sludge is dehydrated.

However, this method does not produce strong flocs depending on the type of amphoteric organic polymer flocculant, so it is not possible to increase the throughput per unit time during mechanical dewatering, and the water content of the dehydrated cake also decreases. There is a problem in that it cannot be lowered sufficiently.

C Problems to be Solved by the Invention] The purpose of the present invention is to solve the above-mentioned problems,
An organic material that has a large sludge processing capacity per unit time, a high recovery rate of SS (suspended solids), good peelability of the dehydrated cake from the filter cloth, and can reduce the water content of the dehydrated cake. The purpose is to propose a method for dewatering sludge.

(! [Means for solving 1g] The present invention provides a method in which an inorganic flocculant is added to organic sludge, and further an amphoteric organic polymer flocculant is added, followed by dewatering. , the colloid equivalent value (a value) at PH3 is 1.0 to 3.7 eq/g, pH 7
The colloidal equivalent value (b value) at -0,35 to -3,
5 eq/g, and the value of (ab)/a indicating the ratio of anion amount/cation amount is 1.2 to 2.0. .

The organic sludge to be treated in the present invention is not particularly limited, but includes, for example, anaerobic digested sludge of human waste, aerobic digested sludge of human waste, human waste septic tank sludge, human waste digested desorbed liquid, sewage, and activated sludge treatment of various industrial wastewater. Examples include organic sludge such as surplus sludge, primary sedimentation tank sludge of sewage, coagulated sludge generated in the tertiary treatment of human waste, sewage, etc., and coagulated sludge of various industrial wastewaters.

Examples of the inorganic flocculant used in the present invention include ferric chloride, aluminum sulfate, aluminum chloride, polyaluminum chloride, and polyferrous sulfate. The amount of these inorganic flocculants added depends on the type of compound used, but it is preferable to add them so that the pH of the organic sludge to be treated is in the range of 3.0 to 5.0. Iron-based inorganic flocculants such as ferric iron and polyferric sulfate are used on p) 13.
5-4.5. Aluminum-based inorganic flocculants such as aluminum sulfate, aluminum chloride, and polyaluminum chloride exhibit the highest addition effect when added at a pH of 4.0 to 5.0. When the pH is large, acid may be added to adjust the pH.

The amphoteric organic polymer flocculant of the present invention has a colloid equivalent value (a value) obtained by colloid titration with PH3, which indicates the amount of cations.
is 1.0 to 3.7 maq/g, and the colloid equivalent value obtained by colloid titration at pH 7, which indicates the difference between the amount of anions and the amount of cations (
b value) is -0.35 to -3.5 rmeq/g, and the value of (a-b)/a, which indicates the ratio of anion amount/cation amount, is in the range of 1.2 to 2.0. use.

Under the condition of pH 3, the anionic groups in the amphoteric organic polymer hardly dissociate, and on the contrary, the cationic groups are thought to mostly dissociate. can be regarded as the total cation content of the amphoteric organic polymer.

On the other hand, the colloidal equivalent value of anion is usually PH10.5
However, in this p)l, the cationic group in the amphoteric organic polymer may be hydrolyzed to become anionic group, so in the present invention, the value titrated at pH 7 is used. In this case, since both the cation group and the anion group in the amphoteric organic polymer dissociate, the result of colloid titration is the amount of extra anion that cancels out the cation and anion.

Therefore, the total anion content in the amphoteric organic polymer is at pH 3.
It can be regarded as the sum of the absolute values of the cation amount titrated at 21!7 and the anion amount titrated at 21!7.

The amount of cations (a) titrated with P113 is expressed as a positive number.

Since the anion ffi (b) titrated with P117 is expressed as a negative number, the total amount of anions in the amphoteric organic polymer flocculant is (ab).

Therefore, (ab)/a used in the present invention is 1.2 to 2.
The amphoteric organic polymer flocculant No. 0 is a flocculant in which more anion groups than cation groups are distributed in two molecules.

The amphoteric organic polymer flocculant that can be used in the present invention includes p
Colloid equivalent value (a) in H3 is 1.0 to 3.7+
*eq/g, the colloid equivalent value (b) at pH7 is -0,35 to -3,5+meq/g, and the anion amount/cation amount ratio ((a-b)/a) is 1.2 to 2. Any amphoteric organic polymer within the range of 0 can be used. Examples of such materials include copolymers of anionic monomer components and cationic monomer components, anionic heptamer components, copolymers of cationic monomer components and nonionic monomer components, or copolymers of anionic monomer components and nonionic monomer components. Examples include Mannich-modified products or Hofmann-decomposed products of copolymers of monomer components and nonionic monomer components.

Examples of anionic monomer components include acrylic acid (A^), sodium acrylate (NaA), methacrylic acid, and sodium methacrylate. Examples of the cationic heptamer component include dimethylaminoethyl acrylate and dimethylaminoethyl (meth)acrylate (DAM).

Examples include dimethylaminopropyl (meth)acrylate and quaternized products thereof.

Specific examples of the quaternized product include dimethylaminoethyl acrylate methyl chloride quaternized product (DAA). Examples of the nonionic monomer component include acrylamide (AA+a).

Examples include methacrylamide, N,N'-dimethyl(meth)acrylamide, and the like. In addition, as a copolymer of these compounds, specifically DAA/AA/A
Am copolymer (for example, molar ratio of 25/35/40)
), DAM/AA/AAm copolymer (25/35/
40), DAA/AA/AAm copolymer (15/25
/60, 20/40/40, 35150/15),
DAA/AA copolymer (40/60), or N
Examples include Mannich modified products of aA/AAa+ copolymers.

The above amphoteric organic polymer flocculants have a zero resistance to SS.
．． It is preferable to add it in a proportion of 4 to 1.0% by weight.

To dehydrate organic sludge according to the present invention, first, an inorganic flocculant is added to the sludge, mixed and stirred, and then an amphoteric organic polymer flocculant is added and mixed and stirred to perform flocculation. Mixing and agitation is not limited to stirring using a stirring blade in a stirring tank, but may also be based on flow in piping. In the case of a stirring tank equipped with a stirrer, the circumferential speed of the stirring blade should be 0.5 to 5 m/s as a guide.
Let it be ee.

Next, the flocs generated by the above agglomeration are used as they are.
Alternatively, after removing the separated water, supply it to a dehydrator and dehydrate it in the same manner as the conventional method. Examples of dehydrators include centrifugal dehydrators,
Conventionally used dehydrators such as a vacuum dehydrator, belt press type dehydrator, screw press or filter press can be used.

The mechanism of action of the dehydration method of the present invention is estimated as follows.

First, inorganic flocculants have very small molecular weights and do not form flocs, so they can sufficiently react with the anionic mucilage on the surface and inside of sludge particles.
Due to the decrease in H, the carboxyl groups of mucilage substances such as proteins and polysaccharides are deionized, thereby neutralizing the charges.

As charge neutralization by the inorganic flocculant progresses, the water held by the sludge particles decreases, and at the same time, the adsorption points where the cationic groups of the polymer flocculant react decrease.

On the other hand, the adsorption of anionic groups and the amount of reacting acidic metal hydroxides increase. For this reason, when a cationic organic polymer flocculant or an amphoteric organic polymer flocculant containing a large amount of cations is used, it becomes impossible to generate flocs strong enough to allow mechanical dewatering. In addition, when anionic organic polymer flocculants are used, the adsorption and reactivity of anionic groups is too large, so
The anionic organic polymer flocculant becomes stuck to one sludge particle, and the anionic organic polymer itself contracts and precipitates, crosslinking and aggregating other particles.

It becomes impossible to form coarse flocs.

On the other hand, when an amphoteric organic polymer flocculant is used, when the anion group reacts and adsorbs to the sludge particles, the flocculant does not stick to the sludge because there is a cation group in the same molecule, and some The group exists in a free state.

The free groups of such amphoteric organic polymer flocculants adsorb each other and crosslink, thereby binding sludge particles and forming large and strong coagulated flocs.

Such coagulated flocs have good dewatering properties, and by mechanically dehydrating them, efficient dewatering treatment can be performed.

〔Effect of the invention〕

As described above, according to the present invention, since dewatering is performed using an inorganic flocculant and an amphoteric organic polymer flocculant in which the amount of anions is greater than the amount of cations, the processing time per unit time is reduced in the dewatering treatment of organic sludge. It is possible to increase the capacity, increase the recovery rate of SS, improve the peelability of the dehydrated cake from the filter cloth, and lower the water content of the dehydrated cake. Therefore, costs such as the fuel necessary for incinerating the dehydrated cake and the cost of transporting the dehydrated cake can be saved.

〔Example〕

Examples of the present invention will be described below. Note that % indicates weight %. Further, the amphoteric organic polymer flocculants used in the Examples and Comparative Examples are summarized in Table 1, and the polymer flocculant compositions used in the Comparative Examples are summarized in Table 2. In each Example and Comparative Example, one selected from the polymer flocculants shown in Table 1 or Table 2 was used.

Example 1 Excess sludge from activated sludge treatment at a sewage treatment plant was subjected to a dewatering test using a belt press filter cloth. Its properties include solid concentration (SS) of 9200 mg/ρ and organic content (vs. 5S) of 83.
The sludge was very difficult to dewater, with a fiber content (relative to 5S) of 0.2%.

In the test, 200 mu of sludge was collected in a 30 On+Q beaker, and an inorganic flocculant and an amphoteric organic polymer flocculant shown in Table 3 were sequentially added and reacted to obtain flocculated sludge. This flocculated sludge was subjected to gravity filtration using a filter cloth with a filtration area of 19.6 aJ, and the liquid volume after 20 seconds was determined by 'JIB.

This operation was performed while changing the amount of the amphoteric organic polymer flocculant added by 4 to 5 points, and the amount added (optimum amount added) at which the amount of gravity filtration filtrate was maximized was determined. 1 gravity filtrate to 0 under the optimum addition amount conditions
．． 5.1.0 or 12 at a squeezing pressure of 1.5 kg/d
The cake was dehydrated by pressing for 0 seconds, and the peelability of the dehydrated cake and the moisture content of the dehydrated cake were measured. The results are shown in Table 3.

Comparative Example 1 The same procedure as in Example 1 was carried out except that the polymer flocculant shown in Table 4 was used instead of the amphoteric organic polymer flocculant used in Example 1. The results are shown in Table 4. 6'Example 2 Excess sludge from the same sewage treatment plant as in Example 1.

Dehydration was performed using a belt press dehydrator, and the water content and amount of the dehydrated cake were measured. The properties of the sludge subjected to the test were as follows: solid content concentration (SS) 8200 mg/Q, organic matter content (
The fiber content (vs. 5S) was 82.6%, and the fibrous content (vs. 5S) was 0.2%.

Ferric chloride was added to the above sludge as an inorganic flocculant so that the iron atoms were 3.2% based on SS (at this time, the pH was 4).
．． 0), and A as an amphoteric organic polymer flocculant.
R-1 was added to SS at a concentration of 0.55% for aggregation treatment.

After the aggregation treatment, dehydration treatment was performed using a belt press dehydrator with a cloth width of 400 mm, and the water content of the dewatered cake and the amount of sludge processed were measured. The filter cloth tension of the dehydrator is 0.
The weight was varied between 5 kg/cd and 1.5 kg/cd to provide stable dehydration cake releasability. In addition, the amount of sludge supplied was increased or decreased, and the filter cloth traveling speed at this time was set to the lowest filter cloth speed at which sludge did not cause site leakage in the gravity filtration vortex section and press dewatering section. The results are shown in Figure 1.

As shown in Figure 1, the standard throughput of a belt press is 1.
00kg-03#t?・Moisture content at h is 75.0%
Met. In addition, when the water content is 80%, the processing amount is 1
It was 98kg-DS/Boh.

Comparative Example 2 The amount of ferric chloride added in Example 2 was changed from 3.2% to 1.6%.
The same procedure as in Example 2 was carried out except that 1.1% of AC-1 was added in place of the amphoteric organic polymer flocculant AR-1. The results are shown in Figure 1.

Comparative Example 3 0.6 CR-2 was used in place of AC-1 used in Comparative Example 2.
The same procedure as Comparative Example 2 was carried out except that 5% was added. The results are shown in Figure 1.

Comparative Example 4 The same procedure as in Example 2 was carried out except that C-t was used alone as a flocculant (the amount added was 0.65% based on SS).

The results are shown in Figure 1.

From Figure 1, the standard processing amount of Comparative Examples 2 and 3 is 100 kg.
-The moisture content in DS/I and h is 81.4%, respectively.
The processing amount at 82.5% and 80% moisture content is 76ktsDS/rrhh and 66kg-DS/bo, respectively.
h, and it can be seen that Example 2 has improved water content by about 7% and has 2.5 to 3.0 times the capacity in terms of throughput.

Example 3 In centrifugal dewatering of sludge from a human waste treatment plant, the maximum throughput at which the solid content recovery rate would be 95% or more was determined.

The properties of the sludge subjected to the test were as follows: solid content concentration (SS) 233
00 mg/ffi, organic content (vs. 5S) 72.8%, and fibrous content (vs. 5S) 6.0%.

Ferric chloride as an inorganic flocculant and AR-1 as an organic polymer flocculant were added to the sludge, and the sludge was rated at 3 m/h (S
Dehydration treatment was performed using a centrifugal dehydrator (in the case of S==20000 mg/Q). The amount of sludge treated gradually increased from 3 m''/h. The amounts of the inorganic flocculant and the amphoteric organic polymer flocculant added were the optimum amounts determined in preliminary tests. The results are shown in Table 5.

Comparative Examples 5 to 6 Example 3 except that CR-2 (Comparative Example 5) or C-2 (Comparative Example 6) was used instead of AR-1 used in Example 3.
I did the same thing. The results are shown in Table 5.

4,

[Brief explanation of the drawing]

FIG. 1 is a graph showing the results of Example 2 and Comparative Examples 2 to 4.

Claims (1)

[Claims] (1) In a method of adding an inorganic flocculant to organic sludge and further adding an amphoteric organic polymer flocculant and then dewatering the sludge,
The amphoteric organic polymer flocculant has a colloid equivalent value (a value) of 1.0 to 3.7 meq/g at pH 3 and a colloid equivalent value (b value) of -0.35 to -3.5 meq/g at pH 7.
q/g, and the value of (ab)/a representing the ratio of the amount of anions to the amount of cations is 1.2 to 2.0.